OBGY Radiology

Case 19

OBGY RADIOLOGY:
MRI GRAVID UTERUS

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(MR
ssFSE T2W images )

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Imaging Finding

Conjoined Twins (Janiceps type)

Fig
1 & 2: MR ssFSE T2W images with fused calvaria and colpocephaly
Fig 3 & 4 : Two pairs of eyeballs (i.e. 4 orbits) in opposite directions
Fig 5 : Fusion of the neck, thorax and abdomen is also seen. Spine is
separate. Two urinary bladders and an umblical cord are seen. The hypointensities
in the liquor consist of parts of extremities and cord as well
as artifacts due to are due to fluid motion.
Fig 6: MR 3D reconstruction model showing Janiceps type of cranio-thoraco-abdominopagus
deformity with two eyes and separate limbs

Discussion

Magnetic resonance
imaging of a moving fetus was always considered difficult because of the
longer scanning time. Ultrafast magnetic resonance imaging with faster
gradients and new software enables rapid imaging of the fetus. This enables
imaging quality superior to two-dimensional ultrasonography and should
be considered an adjunct to ultrasonography for characterization of some
fetal abnormalities (1). MRI has emerged as a useful imaging technique
because of high resolution, ability to characterize tissues and inherent
capability to generate information in three planes (2).

Conjoined (Siamese)
twins are rare with an incidence of 1 in 30,000 to 1 in 1,00,000 births
(3). The frequency is independent of maternal age or parity and it occurs
sporadically. Conjoined twins result from monozygotic twinning when the
embryo does not split until after the second week of gestation (4).

They are classified
according to the location of the tissue that links the twins as craniopagus
(joined at cranium), thoracopagus (joined at the thorax), omphalopagus
(joined at the anterior abdominal wall), pyopagus (joined at buttocks
and lower spine and lying back to back), and ischiopagus (joined at sacrum
and coccyx and lying side to side). Early antenatal diagnosis and assessment
of the rare entity of conjoined twins helps in determination of postnatal
viability, which depends on the organs shared and whether surgical correction
is possible. Many anatomical abnormalities are common among conjoined
twins. Congenital heart disease ( most commonly a ventricular septal defect
or Tetralogy of Fallot ) is present in 75% of thoracopagus twins. The
liver is shared in 81% of omphalopagus twins. In craniopagus twins, the
prognosis depends on the degree of connection between the brains (5).

Janiceps type of
cephalo-thoraco-abdominopagus twins is even more rare. Its incidence is
1 in 3 million conjoined twins (6). It derives its name from Janus, the
god of doors and gateways, his statue with two faces, facing east and
west for the beginning and ending of the day (6,7). Survival of conjoined
twins depends on the presence or absence of associated anomalies. The
surgical challenges include separation of the important shared organs
and closure of defects in bones and soft tissues (2).

Complex congenital
anomalies are optimally evaluated with sonography and magnetic resonance
imaging. With the advent of ultrafast imaging sequences, magnetic resonance
imaging of the fetus is now easier. It allows demonstration of anatomical
details in a three dimensional perspective. Magnetic resonance imaging
is considered to be superior to other modalities in illustrating neurosurgical
abnormalities in craniopagus twins (8). Magnetic resonance imaging simplifies
the work-up of conjoined twins, without the risks of ionizing radiation
or injection of radio-opaque contrast. To assist in planning the separation,
a three-dimensional computer model of the conjoined twins can be constructed
on the basis of the prenatal magnetic resonance imaging studies, as in
our case. This helps the surgeons and the parents to have a better visualization
of the anomaly. Because of the ability of magnetic resonance imaging to
enhance the visualization of abnormal anatomy, the surgeon can deal with
greater confidence and can plan potentially safer operations for all types
of conjoined twins (6).

Magnetic resonance
imaging can be conveniently performed in cases of conjoined twins. It
complements and enhances the diagnosis made on ultrasonography. High resolution
whole body images are useful in counseling the parents on the degree of
abnormalities and the multiplanar images are well understood even by the
non-radiologists. The accurate identification of the extent of fusion
helps rational decision making and planning for the surgery, if possible.